Constraining the Physical Parameters of Coronal Mass Ejections at Large Coronal Heights using Low Radio Frequency Gyrosynchrotron Emission

Abstract:

Coronal Mass Ejection (CMEs) are large scale explosive eruptions of magnetised plasma from the Sun into the Heliosphere. Measuring the physical parameters of CMEs is crucial for understanding their physics and for assessing their geo-effectiveness. Radio observations offer the most direct means for estimating these plasma parameters when gyrosynchrotron (GS) emission is detected from the CME. However, since the first detection by Bastian et al. in 2001, only a handful of studies have successfully detected GS emission from CME plasma.This is usually attributed to the challenges involved in obtaining the high contrast imaging required for observing this faint emission in the vicinity of active solar emissions.

Recent work using data from the Murchison Widefield Array, a low frequency SKA precursor, and the newly developed imaging pipeline designed for solar imaging (Mondal et al., 2019) marks a significant improvement in metrewave solar radio imaging. Our work suggests that we should now be able to routinely detect GS emission from CME plasma. We present an example where we have successfully detected radio emission from CME plasma and modelled it as GS emission, leading to reliable estimates of CME magnetic field as well as the distribution of energetic electrons. In a different example, we find that the observed spectra are not always consistent with simple GS models. For this CME we are able to detect the radio emission from the CME plasma out to as far as 8.3 solar radii. This highlights that more complicated physics might be at play and points to the need for building more detailed models for interpreting these emissions. We note that these are the weakest detections of GS emissions from CME plasma reported yet.